Catalytic cracking of high boiling tar acids



May 22, 1956 M. B. NEUWORTH CATALYTIC CRACKING OF HIGH BOILING TAR ACIDSFiled June 18, 1953 FLUE GAs SOLIDS LIFT I2 OATALYsT REGENERATION 4 24GAs I 22,532 HYDROCARBON I I FDTAR VAPORS PRODUCT OARBON RECOVERYDEPOSITION HYDROCARBON Low BOILING DISTILLATE NEUTRALS INERT DII-UENTNONDISTILLABLE lo RESIDUE HEATER 22 REACTION 32 VESSEL G I REGYCLE HIGHBOILING TAR ACIDS A B HIGH BOILING 49 'figfif z g INERT TAR ACIDSDILUENT ff 48 FLUE 42 HIGH BOILING "Q I GAs 6o HEATER 56 TAR ACIDS 54 IGAS cATALYsT 3 ,LOw BOILING VESSEL PRODUCT TAR ACIDS RECOVERY LOWBOILING NEUTRALS 58 52 NONDISTILLABLE AIR RESIDUE JNVENTOR MARTIN B.NEUWORTH HYDROOARBON VAPORS United States Tatent CATALYTIC CRACKING OFHIGH BOILING TAR ACIDS Martin B. Neuworth, Pittsburgh, Pa., assignor toPittsburgh Consolidation Coal Company, Pittsburgh, Pa, a corporation ofPennsylvania Application June 18, 1953, Serial No. 362,517 Claimspriority, application Great Britain August 6, 1952 7 Claims. (Cl.260--621) like. In conventional processing, tar acids are separated intoa low boiling fraction and a high boiling fraction. The commerciallyvaluable tar acids comprising phenol, cresols, xylenols and mono-ethylphenol, boil below 230 C. All other tar acids can be characterized ashigh boiling tar acids. Thus the term high boiling tar acids comprehendsany and all tar acids boiling above 230 C. and encompasses, for example,polyethyl and higher alkylated phenols, polycyclic phenols, polyhydricphenols and the like.

Low boiling tar acids are generally in greater demand than high boilingtar acids. It is therefore desirable to convert the tar acids boilingabove 230 C. into the less complex and more valuable materials boilingbelow 230 C.

The primary object of the present invention is to provide a new methodof making low boiling tar acids from high boiling tar acids.

According to my invention, tar acids boiling above 230 C. are passed inthe vapor phase at a temperature of about 700 to 850 F. over asilica-alumina catalyst that has deposited thereon a layer of carbonconstituting at least five per cent of the weight of the catalyst. Thereaction is preferably carried out at atmospheric pressure, although thepartial pressure of the tar acids may be reduced by the addition of aninert diluent gas, such as nitrogen, flue gas or the like.

Prior processes have been proposed for dealkylating four-carbon atomalkyl sidechains from alkyl substituted phenols using silica-aluminacatalysts in the liquid phase. These liquid phase processes merelyeffect the removal of a readily removable substituent, namely, afour-carbon atom sidechain. However, it should be pointed out that Ifour-carbon atom sidechains are virtually unknown in raw tar acids,probably because the conditions required for preparing the raw tar aresufiiciently drastic in themselves to dealkylate any existing sidechainscontaining as many as four-carbon atoms.

Silica-alumina is well known commercially as a catalyst for convertinghydrocarbons, and especially petroleum hydrocarbons, in the vapor phase.These reactions convert a portion of the feedstock to carbon which isdeposited upon the catalyst, substantially diminishing its activity.This drastic reduction in activity necessitates regeneration of thecatalyst before the carbon content reaches five per cent of the weightof silica-alumina. Regeneration consists of substantially completelyburning off the deposited carbon to restore the catalyst activity.

Fresh silica-alumina exhibits a high activity and a low selectivitytowards high boiling tar acids, i. e., with fresh silica-aluminacatalyst, high conversions are effected (high activity) but very littleof the converted material is in the form of the desired products (lowselectivity); instead, most of the converted material is carbon, highboiling residue and gas. Hence, if pure silica-alumina (i. e., no carboncoating) were employed as a catalyst for high boiling tar acids,substantial quantities of the tar acids would be converted, but theprincipal products would be carbon, gas and high boiling residue insteadof the desired low boiling tar acids.

I have discovered that high boiling tar acids can be converted into lowboiling tar acids in high yields by contacting vaporized tar acids atabout 700 to 850 F. with a silica-alumina catalyst coated with at leastfive per cent of carbon. High conversions are accompanied bycorresponding high selectivity in my new process.

For a better understanding of my invention and its objects andadvantages, reference should be had to the following description andaccompanying drawings in which:

Figure l is a schematic representation of an apparatus for carrying outmy new process on a continuous basis; and

Figure 2 is a schematic representation of an apparatus for carrying outmy new process in a batchwise manner.

In Figure 1 a moving bed solids contacting unit is provided whichcomprises a reaction vessel 10, a catalyst regeneration vessel 12 and acarbon deposition vessel 13. A bed of silica-alumina catalyst containingat least five per cent by weight of carbon on its surface is maintainedin the reaction vessel 10. Spent catalyst is withdrawn from the bottomof vessel 10 and carried through a solids lift 14 to the regenerationvessel 12. Regenerated catalyst is withdrawn from the vessel 12,conducted to the carbon deposition vessel 13, and then returned to thereaction vessel 10.

A tar acid fraction whose minimum boiling point is greater than 230 C.is introduced in the vapor phase into the reaction vessel 10 throughconduit 18. The temperature of the catalyst in the reaction vessel ismaintained at about 700 to 850 F. The high boiling tar acids may bepreheated to the reaction temperature by a heater 20. If desired, aninert diluent gas, such as nitrogen, flue gas or the like may be addedthrough conduit 22 to the high boiling tar acids in order to reducetheir partial pressure. In general, from zero to ten parts of inertdiluent should be employed. The liquid hourly space velocity (LHSV) forthe reaction is preferably 0.1 to 5.0.

The catalyst in the reaction vessel 10 comprises silicaalumina which hascarbon on its surface amounting to at least five per cent of the weightof silica-alumina. Suitable catalysts for the purposes of this inventioncan be purchased commercially or can be prepared by processes well knownin the art. In general, these catalysts consist essentially of l to 50per cent alumina and 99 to 50 per cent silica; the preferred catalystsfor the present invention are those consisting essentially of 1 to 20per cent alumina and 99 to per cent silica. The carbon on the catalystmay be deposited by treating fresh silica-alumina at elevatedtemperatures with hydrocarbonaceous materials that will react to formcoke on the catalyst particles, as will be more fully described below.

During the cracking of the high boiling tar acids in the reaction vessel10, additional carbon is deposited upon the catalyst from thedecomposition of a portion of the feed material. The selectivity of thecatalyst for the desired low boiling tar acids increases with the carboncontent of the catalyst. However the catalyst activity graduallydecreases with increasing carbon content. Ultimately, the increasedcarbon deposition reduces the catalyst activity to an uneconomic leveland regeneration is required in order to restore the catalyst to ahigher activity level. While the precise value of the carbon content atthis uneconomic level will vary with the treated materials, it generallyis of the order of 20%.

Regeneration is conducted in the regeneration vessel 12 where air isintroduced through a conduit 24 to burn the carbon from the catalyst.Gaseousproducts of cornbustion are removedtrom the system through aconduit 26. These gases can be employed satisfactorily as inert diluentsfor the feed tar acids if desired. I V

The substantially carbon-free catalyst is conducted through a valvedconduit 15 to a carbon deposition vessel 13 Where a fresh coating ofcarbon amounting to at least five per cent of the Weight ofsilica-alumina is deposited. This deposition of carbon may be effectedby passing a low cost hydrocarbon distillate from a conduit 25 throughthe regenerated silica-alumina in vessel.13 at a temperature of 70$) to850 F, and thence to discharge through conduit 27. The distillate isdecomposed and the decomposition is continued until the desired amountof carbon is deposited. The freshly coated catalyst is returned toreaction vessel through valved conduit 16.

vaporized products of the cracking reaction pass from the reactionvessel 10 to a product recovery system 28 through a product conduit 30.Generally the product is separated into fixed gases, such as ethyleneand propylene, low boiling tar acids, low boiling neutral compounds andnondistillable residue. The unconverted high boiling tar acids areseparately recovered and can be recycled to the reaction zone through aconduit 32.

Figure 2 illustrates a fixed bed apparatus for the cracking of highboiling tar acids according to my invention. A reaction vessel 40 isprovided in which a fixed bed of catalyst is maintained. The catalyst issilicaalumina which has carbon deposited thereon amounting to at leastfive per cent of the weight of silica-alumina. The operation of theapparatus is cyclic, with each reaction phase being interspersed with acatalyst regeneration phase. During the reaction phase, high boiling taracids in the vapor form are introduced through a valved conduit 42 intothe catalyst vessel 40 which is maintained at a temperature of 700 to850 F. The high boiling tar acidsmay be preheated to the reactiontemperature in a 'preheater 46. The partial pressure of the high boilingtar acids may be reduced by dilution with an inert diluent gas which isintroduced through a conduit 43. Vaporized products of the crackingreaction are collected through conduit 52 and sent to a product recoverysystem 54. Products are separated into. gases, low boiling tar acids,low boiling neutral compounds and undistillable residue. Unconvertedhigh boiling tar acids can be recycled to the reaction vessel through aconduit 56.

As the cracking reaction proceeds, a portion of the high boiling taracids is converted to carbon which is deposited upon the catalyst. Thecontinued carbon deposition gradually decreases the catalyst activityand necessitates catalyst regeneration when the activity falls below apredetermined level which is relatable to the carbon content. In orderto regenerate catalyst in the system illustrated in Figure 2, the flowof high boiling tar acids into the reaction vessel 40 is terminated byclosing conduit 42. Air is introduced through a valved conduit 58 intothe vessel 40 to burn carbon from the catalyst. Gaseous products ofcombustion are discharged from the system through a valved conduit 60.The air may be diluted with an inert gas, such as nitrogen, flue gas orthe like, in order to prevent excessive temperatures from developing inthe vessel 40 through the combustion of carbon.

Gaseous products of combustion may be used to dilute feedstock for thereaction phase or as a diluent for combustion air in the regenerationphase. When the catalyst is satisfactorily regenerated, conduits 58 and60 are closed. The regenerated catalyst is then prepared for asubsequent reaction phase by coating it with at least five per cent byweight of carbon. For this purpose hydrocarbon distillate is introducedinto vessel 40 through valved conduit 49 and withdrawn through valvedconduit 59.

The process of Figure 2 can be made continuous by providing two or morecatalyst vessels arranged in parallel. By operating the catalyst vesselsalternately in a cyclic manner, the system can be continuously onstreamwith respect to the high boiling tar acids. 7

The results of carrying out the cracking of high boiling tar acids inaccordance with my new process are tabulated in Table I. The tar acidfeed was a 230300 C. boiling range distillate fraction of tar acidsobtained from tars derived from low temperature carbonization ofbituminous coal. Partial pressure of the feedstock was reduced bydiluting it with nitrogen gas. The silicaalumina contained about 88 percent by Weight of silica and about 12 per cent by weight of alumina. Thecatalyst was prepared by passing high boiling tar acids in vapor formthrough a bed of the fresh silica-aiumina at a temperature in the rangeof 700-850 F. until the carbon deposition on the catalyst amounted tomore than live per cent of the Weight of the fresh silica-alumina.

The process was operated according to the method illustrated in Figure2, i. a, batchwise with respectto the catalyst which was maintained inthe fixed bed. The tar acids passed downwardly through the catalystvessel. The abbreviation VMSV means vapor minute space velocity, i. e.,the volume of vapor per volume of catalyst per minute. Its numeral valueis expressed then as min- Table I.230300 C. tar acids Run 1 1 2 3 4Temperature, F 800 800 800 700 VMSV i0. 4 7. G 6.8 Partial Pressure, atmi). 51 O. 35 0. 36 Conversion (Wt. Percent of Feed) 2 32 53 30 Yield Wt.Percent of Converted Feed:

Tar Acids 080-230 C.) 47.2 47.1 37.9 39.4 Neutrals (180230 C.) 3 8. 810. 9 13.4 10. 3 Residue (B. P. above 300 C.) 12. 7 6. 5 8. 9 6. 4 Gus7. 5 6. 7 8.3 3.4 Carbon 23. 8 28. 8 31. 2 40. 9

K Run Number 1 was conducted with a raw distillate ta'r acid fractionwhich had not been freed of tar bases prior to the cracking treatment.gggser runs were conducted with tar acids which had been freed of 1 Anymaterials boiling in the range 230 to 300 C. are reported as unconvertedfeed.

3 Neutrals as reported in Table I are those compounds which remainundissolved in caustic soda during the separation procedure set forth inInd. dz Eng. Chem. 32, 1614 (1940).

The results reported in Table I establishedthat my new process iseifective for converting high boiling tar acids (i. 'e., those boilingabove 230 C.) into low boiling 'tar acids (i. e., those boiling below230 C.). Low boiling neutral oils in the products from my process alsocan be be marketed at an advantage over the high boiling tar acidfeedstock. v

In general, the rate of conversion increases with the temperature andalso with the contact time between the feed material and the catalyst.

It should be noted that my new process will operate to crack tar acidswhich have not been freed of tar bases. This is surprising in view ofthe fact that tar bases are well known as a catalyst poison. Forexample, in run 1, taracids which had not been freed of 'tar bases wereconverted at a rate of 25 percent; the preliminary removal of the tarbases, run 2, increased the conversion to 32 percent under otherwisesimilar conditions,

I have found that the rate of carbon laydown can be reduced by using aninexpensive neutral hydrocarbon distillate fraction as diluent for thehigh boiling t'ar acids. Particularly 1 have found that an effectivediluent is 'the neutral oil derived from the tars produced by low'temper ature carbonization of bituminous coal.

Results of two runs "employin neutral "oil as "diluent are reported inTable II. In runs 5 and 6, 45 parts by weight of 230-300 C. tar acidswere mixed with 100 parts by weight of 160-300 C. low temperaturecarbonization tar neutral oil. The mixture was passed downwardly at LHSVof 1.10 through a fixed bed of silica-alumina which had at least fivepercent of its weight of carbon deposited thereon.

Comparison of run 5 using neutral oil with run 4 shows that the neutraloil results in increased conversion of 230-300 C. tar acids withoutaltering'the yield of low boiling tar acids (180-230" C.) at 700 F.Comparison of run 6 and runs 2 and 3 shows that the addition of neutraloils to high boiling tar acids results in increased conversion withoutsubstantial change in the production of low boiling tar acids (180230C.) at 800 F.

A blank run was carried out in which neutral oil alone was passedthrough silica-alumina catalyst. The carbon laydown from the neutraloils alone was greater than that of the mixture of tar acids and neutraloils under similar conditions of temperature and contact time. Hence,the neutral oil and the high boiling tar acids appear to cooperate toreduce carbon laydown to a value which is less than the sum of thecarbon laid down by each material independently.

It is thus possible to convert the high boiling tar acids in a raw tardistillate fraction into low boiling tar acids without the necessity offirst separating the tar acids from the neutral oils of the tarfraction. Accordingly not only can the costly step of preliminarilyrecovering high boiling tar acids free of neutral oils be obviated, theoverall recovery of valuable low boiling tar acids is thereby increased.Examples of this operation are set forth hereinafter in Table III.

To illustrate my new process as a continuous operation, low temperaturecarbonization tar acid oil was vaporized and passed co-currently througha downwardly moving bed of silica-alumina catalyst having various carboncontents. The tar acid oil feedstock was a 230- 300 C. distillatefraction of raw tar produced by low temperature carbonization ofbituminous coal. Tar acids content of the feedstock was 33.6 percent byweight; neutral oils accounted for substantially all of the rest of thefeedstock. Temperature was 800 F.; LHSV was 0.86 hr.- partial pressureof the tar acid oil was reduced to 0.92 atmosphere by dilution withnitrogen. Results of these experiments are tabulated in Table HI.

Table III Run No 7 8 Average Carbon Content of Catalyst, Wt. Percent 511.5 Conversion of 'Iar Acids in Feedstock, Wt. Percent... 72.9 34. 7Yield of Tar Acids (B. P. range 180-230 C.) Wt. Percent of Converted TarAcids 13. 2 43. 2 Yield. Wt. Percent of 'Iar Acid Oil Feedstock:

Light Oil to 160 C 3. 6 1. 6 160230 C. Distillate 8. 6 9.0 230-300 C.Distillate 64. 6 83. 8 Water 3. 4 1. 2 Carbon 18.6 2. 1 Gas 1.2 1.3 TarAcids Content of 130-230 C D tillate, Wt. Percent 38.1 57. 0

As shown in Table III, it is possible to convert tar acids boiling above230 C. into tar acids boiling below 230 C. in a continuous moving bedprocess. Moreover it is possible to convert these tar acids boilingabove 230 C.

into tar acids boiling below 230 C. without first sepa rating the taracids from the tar acid oil in which they occur. As much as 50 Weightper cent and more of the converted tar acids are those commerciallyvaluable tar acids boiling below 230 C.

The data in Table III also indicate the substantial improvements inproduct distribution which results with increased carbon on thecatalyst. As the carbon content of the catalyst increases: (1) theconversion rate decreases; (2) carbon is laid down at a reduced rate;(3) the conversion of feedstock to low boiling distillate increases; (4)the tar acids content of the low boiling distillate increases; and (5)the amount of distillate available. for recycle increases. v

The foregoing description of the preferred embodiment of my'inventiondiscloses silica-alumina catalysts consisting of silica and alumina.However, it is to be understood that silica-alumina catalysts ascommercially obtainable maycontain minor amounts of other oxides such asmagnesia, boria and zirconia. Since it is essential for the purpose ofthis invention that the catalyst be principally silica and alumina, theamount of other oxides should preferably be kept below ten per cent byweight.

According to the provisions of the patent statutes, I have explained theprinciple, preferred construction, and mode of operation of my inventionand have illustrated and described what I now consider to represent itsbest embodiment. However, I desire to have it understood that, withinthe scope of the appended claims, the invention may be practicedotherwise than as specifically illustrated and described.

I claim:

1. The method of converting tar acids boiling above 230 C. into taracids boiling below 230 C. which comprises passing a mixture boilingabove 230 C. and containing tar acids and neutral oils in the vaporphase at a temperature of 700 to 850 F. through a catalyst consistingessentially of 1 to 50 weight per cent alumina and 99 to 50 weight percent silica, said catalyst having carbon deposited thereon in an amountwhich is at least five per cent by weight of the silica and alumina, andcollecting the vaporized products.

2. The method of converting tar acids boiling above 230 C. into taracids boiling below 230 C. which comprises passing a mixture boilingabove 230 C. and containing tar acids and neutral oils in the vaporphase at a temperature of 700 to 850 F. through a catalyst consistingessentially of 1 to 20 weight per cent of alumina and 99 to per centsilica, said catalyst having carbon deposited thereon in an amount equalto at least five per cent by weight of the silica and alumina, andcollecting the vaporized products.

3. The method of treating tar acid oil containing tar acids and neutraloils derived from the tar produced by low temperature carbonization ofbituminous coal and boiling above 230 C. which comprises passing saidtar acids in the vapor phase at a temperature of 700 to 850 F. through asilica-alumina catalyst having carbon deposited thereon in an amountequal to at least five per cent by weight of the catalyst, andrecovering the product vapors.

4. The method of treating a 230 to 300 C. boiling range distillatefraction of raw tar containing tar acids and neutral oils which has beenderived from the tar produced by low temperature carbonization ofbituminous coal, which comprises passing said distillate fraction in thevapor phase at a temperature of 700 to 850 F. through a silica-aluminacatalyst having carbon deposited thereon in an amount equal to at leastfive per cent by weight of the catalyst, and collecting the resultingvapors.

5. The method of treating tar acids boiling above 230 C. which comprisespassing said tar acids in admixture with neutral oil in the vapor phaseat 700 to 850 F. through a bed of silica-alumina catalyst having carbondeposited thereon in an amount equal to at least five per cent by weightof the catalyst, and collecting the product vapors.

6. The method of converting tar acids boiling above 230 (3. into taracids boiling below 230 C. which comprises passing the vapors of the taracids boiling above 230 C. in admixture with neutral oil vapors througha reaction zone containing a bed of silica-alumina catalyst havingcarbon deposited thereon in an amount equal to at least five per cent byweight of the catalyst, maintaining the temperature of said reactionzone between about 700 and 850 F., collecting the product vapors,withdrawing high carbon content catalyst from said reaction zone,regenerating said withdrawn catalyst by burning the carbon depositedthereon, thereafter depositing a fresh layer of carbon on theregenerated catalystin an amount equal to at least five per cent byweight of the catalyst, and returning the resulting carbon coatedcatalyst to said reaction zone to repeat the above steps.

7. The method of converting tar acids boiling above 230 C. into taracids boiling below 230 C. which comprises passing a mixture boilingabove 230 C. and con E taining tar acids and neutral oils in the vaporform through a reaction zone containing a bed of silica-alumina catalysthaving carbon deposited thereon in an amount equal to at least five percent by weight of the catalyst, maintaining the temperature of saidreaction zone between about 700 and 850 F., collecting the productvapors, withdrawing high carbon content catalyst from said reactionzone, regenerating said withdrawn catalyst by burning at least a portionof the carbon deposited thereon, and returning regenerated catalysthaving a layer of carbon thereon amounting to at least five per cent ofthe weight of the catalyst to said reaction zone to repeat the abovesteps.

References Cited in the file of this patent UNITED STATES PATENTS2,372,018 Ruthruff Mar. 20, 1945 2,394,978 Brandon Feb. 19, 1946 FOREIGNPATENTS 874,911 Germany Sept. 4, 1952

6. THE METHOD OF CONVERTING TAR ACIDS BOILING ABOVE 230* C. INTO TARACIDS BOILING BELOW 230* C. WHICH COMPRISES PASSING THE VAPORS OF THETAR ACIDS BOILING ABOVE 230* C. IN ADMIXTURE WITH NEUTRAL OIL VAPORSTHROUGH A REACTION ZONE CONTAINING A BED OF SILICA-ALUMINA CATALYSTHAVING A CARBON DEPOSITED THEREON IN AN AMOUNT EQUAL TO AT LEAST FIVEPER CENT BY WEIGHT OF THE CATALYST, MAINTAINING THE TEMPERATURE OF SAIDREACTION ZONE BETWEEN ABOUT 700 AND 850* F., COLLECTING THE PRODUCTVAPORS, WITHDRAWING HIGH CARBON CONTENT CATALYST FROM SAID REACTIONZONE,